code: def data_nominal(self):
      data = pd.DataFrame(
          {
              "attr_nominal": [
                  "water",
                  "wine",
                  "beer",
                  None,
                  "wine",
                  "water",
              ],
              "attr_nominal_spaces": [
                  "red wine",
                  "hard liquor",
                  None,
                  "mate",
                  "hard liquor",
                  "mate",
              ],
          }
      )
      return data, "test_nominal", EXPECTED_1.copy()
  
file_path: scikit-survival/tests/test_io.py
imports: from collections import OrderedDict
  from io import StringIO
  import numpy
  import pandas
  import pandas.testing
  import pytest
  from sksurv.io import loadarff, writearff
  from sksurv.testing import FixtureParameterFactory
label_desc: Use image node_id 1 for calling the DataFrameCases obj's underlying member method code with example usage: obj.data_nominal() and returns: data,  str,  EXPECTED_1